How to manage humidity

In Understanding Humidity we explained the reasons for Galicia’s humidity problem. In this second part we give you practical advice on how to manage your Galician property so it doesn’t suffer from high humidity and its related problems.

Essential equipment

First off, it’s essential to know your enemy (and sometimes your friend), and for that you need an indoor/outdoor hygrometer (humidity meter) to see the humidity level inside and out. These can now be had for around £30, and here’s an example on ebay. What you need to know is temperature indoors and outdoors and relative humidity indoors and outdoors (so don’t buy a unit that only shows indoor relative humidity).

Using nature whenever possible

Using your hygrometer you now need to be in a permanent state of “good air alert”! This means watching for air that, when heated to your internal temperature, is of significantly lower relative humidity. Whenever you spot “good air”, which is normally early mornings and when there is a rare wind blowing in from La Meseta (Spain’s high central plain) to the southeast, open all the windows and air your house thoroughly.

Here’s an example:

Inside we have 17.3 C and a current relative humidity level of 57%. Outside it’s 10.8 C and 71%. To compare the two we need to use the chart from Understanding Humidity, as follows:

  1. Track from the outside temperature (10.8 C) to the line matching the outside relative humidity reading (71%).
  2. Follow horizontally across to the current inside temperature (17.3 C)
  3. Scan the relative humidity lines to see what the relative humidity of that air once heated to the current inside temperature will be.

…and the answer in this example is around 46%. This is significantly less than the current inside relative humidity of 57% so this is GOOD AIR and you need to open up your windows and ventilate the house thoroughly with it (obviously turning off any heating while you do this). Keep an eye on the inside relative humidity reading (the hygrometer should be somewhere not near a window, by the way) and once this gets near (say 48-50% in this example) to the calculated value close the windows and turn the heating back on.

Monitor this constantly and do this whenever you can, often with several cycles within a few hours to help dry furniture and structure – it’s a running battle and every cycle of this you do gets moisture out of your house and allows possessions, furniture and building structure to become a little drier.

The graph above is colour coded for a typical inside temperature of 19 C and has three humidity levels shown on it, 45% (ideal), 65% (about as high as you can go without problems), and 80% (when problems start getting severe) for basic use. If you want to be more advanced google image search “Carrier psychrometric chart”…

Don’t make things worse!

A second vital component of using nature to help combat high relative humidity is to introduce as little moisture into the house as possible. Showers, kitchen hobs and human breathing/perspiration can’t be avoided in a house, but drying laundry and non vented conventional tumble dryers inside can. If you have to dry clothes inside then you need a condensation type dryer.

If I open the windows won’t I lose all my expensive heat?

You lose a little, but it’s a price well worth paying. You also probably lose much less than you think because the heat in your house is distributed according to mass: in a typical bedroom of 4 x 3 x 2.5 metres there is around 38kg of air. Compare this with the combined weight of all the furniture, possessions and structure (walls, floor and ceiling), which are also at the same inside temperature, and you find that doing a complete air change in a room probably only loses a couple of percent of the heat energy in it. Once you close the windows the furniture and structure will heat the new air up to almost the original temperature quite quickly.

Is it enough with the natural method?

In (coastal) Galicia, sadly not, for the reasons covered in Understanding Humidity. Throughout the year there are many quite long periods where the humidity is at 85%+, and these are often accompanied by comparitively warm temperatures.
To continue the example above, if we had an outside temperature of 13 C with 85% relative humidity we can calculate that that air would be at 66% humidity if heated to the inside temperature of 17.3 C. That’s higher than the relative humidity of the air currently in the house (57%), so keep the windows shut because we don’t want what’s outside.

The problem is that all houses leak air to some degree, plus human activity (breathing, perspiring, showering and cooking) adds significantly to the inside relative humidity very quickly, and so we need the first two additional weapons in our armoury:

  1. Extractors in the kitchen and bathroom: extractors are a necessity anywhere in the world for these two moisture producing rooms, but doubly so in Galicia where the fight against humidity is so constant. Simply shutting the door and opening a window isn’t a very good alternative as even with the door shut that will actually blow a fair portion of the warm, moist air produced through into the rest of your house. In the absence of any of the whole house systems detailed below it is a necessity to have a good capacity extractor fan mounted high up as near the areas producing moisture (shower, hob) as possible and venting externally.
  2. At least one dehumidifier: dehumidifiers typically cost £100-300 and come in two types, condensation (standard) and dessicant (work better than condensation type at low temperatures). These are very useful to give an extra few % less relative humidity generally or to dry rooms with a specific need or issue (including any bedrooms of people with a dust mite allergy).

Fix your building against humidity

So far we’ve concentrated on humidity coming from the air and people, and that’s a hard enough fight in Galicia on its own. Humidity also gets into a house via floors with no damp proof membrane and from leaking roofs, drains, chimneys, etc. and this should always be fixed as well as possible as soon as possible.

Read our sections on construction for health and comfort , stone walled construction solutions and concrete framed construction solutions for more information about fixing damp ingress problems in typical Galician properties.

Bigger and better solutions

As above, extractor fans in wet rooms are essential to avoid humidity problems, but if it fits in with building restoration plans and if you can afford it there are some bigger and better solutions.

Ground floor damp proof membrane/moisture barrier: most Galician properties have a ground supported concrete ground floor, and the majority have no form of damp proofing whatsoever, unless you count tile glaze. Retrofitting a damp proof membrane is a massive job, although well worthwhile if at all possible, but if your property has any scope for fitting drainage round the sides of the house and/or for fitting a floating floor with damp proof membrane over an existing tiled floor then this can help significantly with humidity and also building health and comfort.
Galiciaproperty offers consultations for this at a low hourly rate as part of its survey service.

Whole house ventilation systems: these systems actively extract and pump air into an out of rooms throughout the house via a network of ducts. Advanced versions can include the following options:

  1. Air input dehumidification: air that is pumped into the house runs through a dehumidifier first.
  2. Air conditioning: air that is pumped into the house can be heated or cooled first.
  3. Heat recapture: the heat energy present in (moist/stale/odorous) air pumped out of the house can be recaptured and put into the fresh air pumped into the house to lower heating costs.
  4. Intelligent control: control systems can analyse the relative humidity and temperature of input and output air and adjust flow rates accordingly for better results and lower running costs.

Unfortunately retrofitting a ducted system involves some significant disruption (holes in walls, ceilings and floors), but the results often justify it.

Heating by conduction, not convection: conventional (ie. radiators) heating systems work by using small, very hot radiators to heat air which then heats the surrounding furniture and structure. This is a convection based model and it really isn’t a good way to heat a house in Galicia, or anywhere else for that matter. You can read more about why on our Constrution for Health & Comfort page.

A conduction based system, which is normally uses underfloor heating, heats the furniture, structure and occupants of the room directly rather than indirectly (using heated air), and this method of heating works well with good levels of ventilation.
When furniture and structure are relatively warmer than the surrounding air they heat up the air immediately in contact with them, its relative humidity drops, and that air then becomes better at removing moisture from the surfaces of the furniture and structure, which is what is important to prevent the problems associated with high humidity.
Water based underfloor heating combined with solar collector panels (ie. heat water, don’t produce electricity) is a great solution for Galicia but it normally requires digging up the entire ground floor and everything built on top of it and so is only suitable for new builds and total renovation projects.
Electric mat underfloor heating is a lot less efficient and therefore a lot more expensive to run, but does provide the same benefits of a conduction based system, but even that requires laying at least a new floating floor (which is a great way to cover 1970s Galician tiling!).
The easiest and cheapest heating system which is primarily conduction is using infra red emitting radiators. In the same way that the sun heats you without heating the air much on a cold but bright day, this new type of radiator heats furniture, structure and occupants using infra red. You can now find these radiators in Spain at very cheap prices from Trotec.

You can find more information about modern heating systems on our eco building page.

Galiciaproperty is happy to help design a bespoke system to manage humidity in your property and arrange quotes from a specialist installer to fit it. Contact us via our plan and manage service page.